POJ_3258_River_Hopscotch(NOIP_2015_D2T1)

 1 #include<cstdio>
 2 #include<algorithm>
 3 using std :: sort;
 4 
 5 const int maxn=50005;
 6 int n,l,m;
 7 int a[maxn];
 8 
 9 void init()
10 {
11     scanf("%d%d%d",&l,&n,&m);
12     for(int i=1;i<=n;i++) scanf("%d",&a[i]);
13     sort(a+1,a+n+1);
14     a[n+1]=l;
15 }
16 
17 bool C(int x)
18 {
19     int last=0;
20     for(int i=1;i<=n-m;i++)
21     {
22         int now=last+1;
23         while(now<=n&&(a[now]-a[last])<x) now++;
24         if(now>n) return false;
25         last=now;
26     }
27     if(a[n+1]-a[last]<x) return false;
28     return true;
29 }
30 
31 int bsearch(int x,int y)
32 {
33     while(x<y)
34     {
35         int m=x+(y-x+1)/2;
36         if(C(m)) x=m;
37         else y=m-1;
38     }
39     return x;
40 }
41 
42 void solve()
43 {
44     int INF=l/(n+1-m);
45     int ans=bsearch(1,INF);
46     printf("%d\n",ans);
47 }
48 
49 int main()
50 {
51     freopen("river.in","r",stdin);
52     freopen("river.out","w",stdout);
53     init();
54     solve();
55     fclose(stdin);
56     fclose(stdout);
57     return 0;
58 }